1. Field of the Invention
This invention relates to thrust vectoring for a ducted propulsion system and, more particularly, a rotatable disc located in the throat of a choked flow nozzle which vectors the engine thrust by being rotated to various angles.
2. Description of the Prior Art
Any vehicle propelled through a medium must have a means to control its direction of travel. Directional control systems are comprised essentially of means for selectively rotating the vehicle about three normal axes, with all three axes being relative to the center of gravity of the vehicle. Rotation about the axial axis is called roll, rotation about the lateral axis is called pitch, and rotation about the vertical axis is known as yaw.
This invention is directed to controlling yaw. However, as will subsequently become clear, it could alternatively be used to control or effect pitch if its axis of rotation were itself rotated by 90.degree. from the orientation shown in the described embodiment.
The conventional device for controlling yaw for a flight vehicle is a vertical stabilizer and hinged rudder located aft of the vehicle's center of gravity. The rudder typically comprises the aft section of the vertical stabilizer. The stabilizer and rudder project radially outward from the external skin of the vehicle. Use of this apparatus causes an increase in skin friction drag and pressure drag for the vehicle, compared to what the magnitude of these drag components would be if the vehicle had no such projecting structure.
The surface area of the rudder must be adequate to provide sufficient force to control yaw at the minimum flight velocity of the vehicle. However, this area is more than enough to control the vehicle at higher velocities, and thus results in excessive drag at velocity greater than the minimum flight velocity. The rudder must also have sufficient area to provide the vehicle with the desired degree of maneuverability. Again, designing the rudder to have the capability of providing the desired degree of maneuverability penalizes the vehicle with drag when the capability to maneuver is not being fully utilized.
One approach to this problem has been to place a hinged rudder or rotatable vane in the exhaust housing of a ducted engine. This results in a smoother aerodynamic shape for the external skin. However, when the exhaust flow is supersonic, the placement of a rudder or rotatable vane in supersonic flow creates shock waves which reduce the thrust as well as the control force which would otherwise be generated by a given rudder deflection.
Examples of the use of a rotatable rudder or vane to deflect flow downstream of the throat of a nozzle are shown in U.S. Pat. No. 3,970,253 issued to William M. Burkes and William H. Miller, in U.S. Pat. No. 3,743,184 issued to H. Vincent Mancus, and in U.S. Pat. No. 3,774,868 issued to Gerald F. Goetz.